Constant frequency wave source



D ec. 16, 1930. w. A, MARRISON 1,784,844

CONSTANT FREQUENCY WAVE SOURCE Filed Oct. 18, 1927 @y @QF/9M A rra/awry Patented Dec. 16, 1930 UNITED STATES PATENT oFFlcE WLEEEN A. mmusoN, or o EANoE, NEW JERSEY, AssIoNoE. 'ro BELL TELEPHONE VLABO1z.a'1o1i.1 1-:s,.INcomomvrEn or NEW Yonx, N. Y., A conrom'rxoN or NEW YORK i' Appcman inea october 1s, 1921. semi No. 225,831.

This invention relates to vconstant frcquency wavesources and more particularly to oscillators and generators including mechanical vibratory systems.

An object of the invention is to com iensate for the eliect of circuit variations w iich tend to vary the amplitude. ol' vibration of the mechanical system.

As is well rerogui'/.ed` lhe`l`i1`a|ueiufy ol' a tuning fork or other mechanical vibrating system is to sonic extent dependent upon the. amplitude of vibration so that when such a device is sustained in vibration by the use of some well-known arrangement,-l'or example, an amplifier coupled with the driving and controlling magnets of a fork, the frequency of .vibration will be. dependent upon the'amplitude of the wave suppliedto the driving "element, f

Ina specific preferred embmliinent this in-` vention comprises 'a tuning fork oscillator of -the type employing un electric discharge amplilier'coupling the controlzaml driving magnets ofthe fork in which there is provided. an electromagnet liaviug a U-shaped coro member mounted with its pole faces in elosepmximity to tbe tine'ends of the fork and having a winding connected in the plate. circuit of the amplifier. 'lhe action of the magnet is to eli'cctively slill'en the tim-s of the fork and produce. an increase in the rate of vibration so that the. frequency of the fork is controlled by the magnitude of the magnetic-field'. Therefore., since the energizing current is proportional to the amplitude of the wave supplied to the driving magnet, by properly adjusting the constants of the. circuit, the fork can be made to vibrate with a substantially constant amplitude hulependent of the driving force, thus preventin any variation in frequency from that e ect.

This invention can be morereadily understood by reference to the following detailed description in connection with the drawing which shows one embodiment thereof in a .tuning fork oscillator.

winding of the control element is connected to the grid circuit of a three-electrode electric discharge device 12S and the windin of the driving element is connected to the p atc circuit thereof through the output transfornie'r14.-

As is well understood in the. art, the fork is maintained in vibration by means of the coupling between the two elements through the discharge device 13. 'l`he vibration of the fork sets up an clectromotive force in the winding of the control element ll, which is impressed on the. grid circuit of the device 13 and ainplilied energy is supplied from its plate circuit to the winding of the driving clement 12. i

'lbe clmetromotive force generated in the winding of the control element 11 is also impressed upon the grid circuit of a second three-elertrmleelectric discharge device l5 and amplilied energy is transmitted to a load circuit through the output transformer 16.

Heating current is supplied to the cathodes of the device 18 and 15 in series from a battery 17 and space. current is supplied to both devices from a battery 18.

Resistances 1f) and 2.0 are employed to provide. a biasing potential for the grid of the device. 12S. 'Ihey are so proportioned as to maintain the. output ofthe device. ll constant irrespective of normal luctuatons of the cathode heating current.

'l`he fork Vis provided with a stiffness control element of the type described and claimed in U. S. patent to Clokey 1,717,094, granted .lune ll, 192i). This element comprises an elcctromaglict 21 having a winding 22 rigidly mounted with its pole faces in alignment with the ends of the tines of the fork. The magnetic ell'ect, due to the energization ofthe electromagnet by current flowing in the winding 22, serves to increase the ell'ective stiffness of the fork and thereby provides a means by which the rate'of vibration may be controlled as hereinafter explained.

The winding 22 is connected in series with a variable resistance 23 through the space current battery 18. Any fluctuations in the voltage of the battery, which would othereffect of the electromagnet21, which causes a consequent decrease in the effective stiffness of the fork, which tends to decrease the rate of vibration in such manner as to compensate for the effect of the decrease in driving forcef- A similar compensating effect is produced by increases in thevoltage of the battery 18, so that the rate of vibration -of the-fork and hence the frequency of theoscillations generated is maintained constant irrespective of fluctuations in the voltage.-

The electromagnet 21 is so spaced with respect 'to the ends of the tines ofthe fork that by an adjustment of tlieresistance 23 a maximum change in absolute value of frcquency can beobtained for a given loss in compensation. This spacing is not very critical and in one embodiment a distance of about 1.5 mm. was found satisfactory.

What is claimed is:

1. A source of constant frequency waves comprising a mechanical vibratory member, means for driving said member, and means responsive to changes in the driving force for controlling the period of vibration of said .member so -that .it is substantially constant during such change.

2. A source of constant frequency waves comprising a mechanical vibratoiy member, electromagnetic means for driving said member, and electromagnetic means responsive to 'changes in the driving force for controlling the period of vibration of said member so that it is substantially constant during such changes.

3. A source of constant, frequency waves comprising a mechanical vibratory member, electromagnetic means for driving said meinber, electromagnetic means comprising a core cooperating with said member to constitute a magnet-ic circuit and a winding on said core, said second mentioned means acting to control the period of vibration of said fork, and an electrical source for supplyin current to said driving means and sald win ing.

4. A source of constant frequency waves comprising a tuning fork, an amplifier, a source of potential for energizing said amplifier, a control element for producing an electromotive force of frequency proportional to the rate of vibration of said fork connected to the input of said amplifier, means for driving saidfork connected to the output of said amplifier, electromagnetic means comprising a core forming with said fori: a magnetic circuit and a winding on said core, said electromagnetic means acting to control the effective stiffness of said fork, and connections from'said source to said Winding to maintain the frequencyof vibrationof said fork substantially constant irrespective of variations ofthe potential of said source.

5. A source of constant frequency waves comprising a tuning fork, an electric ldis'- charge amplifier, a source of space current for lsaid amplifier, an electromagnetic control element for producing an electromotive force of frequency proportional to the rate of vibration of saidv fork connected to the input of said amplifier, `electromagnetic means for driving said fork connected to the Output of said amplifier, electromagnetic meansA comprising a substantially U-shaped core mounted in alignment with the tines of said fork and a winding mounted on said core, said last mentioned means acting to control the effective stiffness of said fork, and connections from said space current source to said winding to maintain the frequency of vibration of said fork substantially constant irrespective of variations of the potential of said source.

6. The method of maintaining the rate of vibration of a mechanical vibratory member substantially constant irrespective of variations in the driving force which comprises subjecting said member to a magnetic force tending to increase the period of vibration of the member and causing said magnetic force to be proportional to the driving force.

7. The method of maintaining the rate of vibration of an electrically driven tuning fork substantially constant irres ective of variations in the driving force w ich comprises magnetically damping the vibrations of said fork and thereby increasing the rate of vibration of thc for and automatically controlling the damping effect to make it proportional to the driving force.

In Witness whereof, I hereunto subscribe my name this 17th day of October, A.

WARREN A. MARRISON. 

